Tubular metal body, method of producing same, liner for pressure vessel and method of producing same

ABSTRACT

A tubular metal body  1  comprises a tube  2  extruded through a porthole die and composed of a plurality of components  2   b  joined to one another with a plurality of joint portions  2   a  extending over the entire length of the tube. The base material metal of the extruded tube  2  in each of the joint portions  2   a  is subjected to a modifying treatment to produce finely divided crystal grains. The modifying treatment for the extruded tube  2  is conducted preferably by frictionally agitating each joint portion using a probe  8  of a friction agitation joining tool  6 . The tubular metal body  1  is available with an increased length in a larger size and has high pressure resistance.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is an application filed under 35 U.S.C. §111(a)claiming the benefit pursuant to 35 U.S.C. §119(e) (1) of the filingdate of Provisional Applications No. 60/469,002 and No. 60/469,023 eachfiled May 9, 2003 pursuant to 35 U.S.C. §111(b).

TECHNICAL FIELD

The present invention relates to tubular metal bodies for use inhigh-pressure piping, for example, for motor vehicles, houses, transportmachines, etc. for passing therethrough fuel hydrogen gas or natural gasof high pressure serving as a fuel for power generation and to a methodof producing the same.

The present invention relates also to liners for use in pressure vesselsfor storing hydrogen gas or natural gas serving as a fuel for powergeneration, for example, in motor vehicles, houses, transport machines,etc. or for use in pressure vessels for storing oxygen gas in oxygen gassupply systems and to a method of producing the liner.

BACKGROUND ART

Widely used as tubular metal bodies are electro-resistance-welded tubeswhich are made by forming a metal sheet into a tubular form by rollforming and joining portions thereof butted against each other byhigh-frequency welding.

Since the weld of the electro-resistance welded tube has a reducedstrength by being thermally affected, the weld is susceptible to fatiguefracture due to stress concentration. The use ofelectro-resistance-welded tubes in pressure piping systems for passing ahigh-pressure gas has not been approved presently.

Accordingly, tubes extruded with use of a mandrel (hereinafter referredto as “mandrel-extruded tubes”) or tubes extruded through a porthole die(hereinafter referred to as “porthole die-extruded tubes” or“die-extruded tubes”) appear useful for pressure piping systems.

However, mandrel-extruded tubes are likely to have an uneven wallthickness and moreover have the problem that these tubes are notavailable with a large diameter and/or in a large length. Anotherproblem encountered is that they can not be obtained if having a complexcross sectional shape. These problems may be overcome with portholedie-extruded tubes, whereas these tubes have the following problem. Thedie-extruded tube is produced by temporarily separating a flow of metalmaterial from a billet into portions at the port part of a porthole dieand joining the separated metal material again at the chamber part. Thetube comprises a plurality of components as joined to one another with aplurality of joint portions extending over the entire length of thetube. Since the joint portions are inferior to the tube components inmechanical properties such as strength and elongation, the tube islikely to fracture at the joint portion owing to stress concentrationwhen used in pressure piping.

It is thought that the die-extruded tube can be made usable for pressurepiping systems when the joint portions are modified in properties.Various heat treatments are known for the billets to be used forextrusion in order to improve the corrosion resistance of the jointportions of porthole die-extruded tubes (see the publication of JP-A No.1999-172387).

However, methods of improving the mechanical properties of the jointportions still remain to be developed, and die-extruded tubes have notbeen placed into use for pressure piping systems.

On the other hand, the high-pressure gas to be contained in pressurevessels like those above-mentioned generally has pressure of about 20 toabout 35 MPa at present, whereas the pressure will presumably be raisedto about 70 MPa in the future.

A liner already known for use in such pressure vessels is produced froma cuplike blank of aluminum by ironing the body of the blank axiallythereof by flow forming to make a headplate portion at each of oppositeends of a hollow cylindrical trunk, closing at least one of the headplate portions to give a larger wall thickness to the head plate portionthan the trunk and forming a mouthpiece mount bore in a closure portionprovided centrally of the head plate portion (see the publication ofJP-A No. 1999-104762, claim 1).

However, this pressure vessel liner has the problem of necessitating acumbersome machining operation and failing to have an increased lengthand a larger size.

Also known is a liner for pressure vessels which comprises an extrudedtubular body of aluminum and head plates welded to respective oppositeends of the body (see the publication of JP-A No. 1999-104762, FIG. 7).Useful as the extruded tubular aluminum body is a mandrel-extruded tube,porthole die-extruded tube, or the like.

The mandrel-extruded tube or die-extruded tube nevertheless has theproblem described with reference to the pressure piping, and thedie-extruded tube has not been placed into use as the trunk of the linerfor pressure vessels.

An object of the present invention, which has been accomplished in viewof the foregoing situation, is to provide a tubular metal body which canbe of increased length and greater size and which has outstandingpressure resistance, and a method of producing the same.

Another object of the invention is to provide a pressure vessel linerwhich can be of increased length and greater size and which hasoutstanding pressure resistance, and a method of producing the same.

SUMMARY OF THE INVENTION

The present invention provides a tubular metal body comprising a tubeextruded through a porthole die and composed of a plurality ofcomponents joined to one another with a plurality of joint portionsextending over the entire length of the tube, the base material metal ofthe extruded tube in each of the joint portions being subjected to amodifying treatment to produce finely divided crystal grains.

Thus, the tubular metal body of the present invention comprises aporthole die-extruded tube composed of a plurality of components joinedto one another with joint portions extending over the entire length ofthe tube. The metal of the tube as the base material thereof in each ofthe joint portions is subjected to a modifying treatment to producefinely divided crystal grains. Accordingly, the joint portions areimproved in mechanical properties, such as strength and elongation, andin corrosion resistance, giving the tubular metal body high pressureresistance. Even if the metal body is used as a pressure tube, forexample, in pressure piping for passing a high-pressure gastherethrough, the joint portions are prevented from fracturing. Thetubular metal body is uniform in wall thickness and can be given anincreased length or a greater size. Furthermore, the tubular body can beof complex cross sectional shape.

With the tubular metal body of the invention, the modifying treatmentfor the extruded tube is conducted preferably by frictionally agitatingeach joint portion using a probe of a friction agitation joining tool.

With the tubular metal body of the invention, it is desired that theextruded tube be fixedly provided inside thereof with a reinforcingpartition extending longitudinally of the tube so as to divide inside ofthe extruded tube into a plurality of spaces. The reinforcing partitionis joined to the extruded tube by friction agitation at at least twojoint portions, or is provided integrally with the components of theextruded tube. When the tube fixedly has the reinforcing partitionprovided therein and extending longitudinally thereof so as to dividethe interior thereof into a plurality of spaces, the tubular metal bodyis given further improved pressure resistance.

The present invention provides a method of producing a tubular metalbody characterized by preparing a tube extruded through a porthole dieand comprising a plurality of components joined to one another with aplurality of joint portions extending over the entire length of thetube, placing a probe of a friction agitation joining tool from outsideinto each of the joint portions of the extruded tube so as to positionthe probe partly in the tube components on opposite sides of the jointportion, and thereafter moving the extruded tube and the probe relativeto each other longitudinally of the tube to thereby frictionally agitatethe base material metal of the extruded tube for a modifying treatmentto produce finely divided crystal grains.

The tubular metal body can be produced relatively easily by the methodof the invention.

In the tubular metal body production method of the invention, it isdesired that the base material metal of the tube as extruded from anextruder be frictionally agitated in the joint portions immediatelyafter extrusion. The tubular metal body can then be produced at a higherrate to achieve a higher production efficiency than when a portholedie-extruded tube having its temperature lowered to a cold working levelis used. The reason is that in the case where the base material metal ofthe die-extruded tube having its temperature lowered to a cold workinglevel is frictionally agitated, it takes time for the frictional heatgenerated by the rotation of the probe to soften the tube at the jointportion and in the vicinity thereof. Further when the base materialmetal of the tube as extruded from the extruder is frictionally agitatedimmediately after extrusion, it becomes possible to subject the tubularmetal body produced to a uniform solution heat treatment to result instabilized mechanical properties. In the case where the base materialmetal of the die-extruded tube as cooled to the cold working temperatureis frictionally agitated, the temperature of the tube rises locally atthe joint portion and in the vicinity thereof to entail the likelihoodthat the tubular body produced will be subjected to an uneven solutionheat treatment. Additionally in the case where the base material metalof the tube as extruded from the extruder is frictionally agitatedimmediately after extrusion, this operation eliminates a faulty jointthat would be produced between the components of the tube in the initialstage of extrusion.

With the tubular metal body production method of the invention, theextruded tube may have a reinforcing partition placed therein andextending longitudinally of the tube so as to divide inside thereof intoa plurality of spaces. In frictionally agitating the base material metalof the extruded tube in each of the joint portions thereof, the forwardend of the probe is then placed into the partition through each of atleast two of the joint portions to join the partition to the extrudedtube by friction agitation. The extruded tube may have a reinforcingpartition interconnecting at least two of the components thereof andextending longitudinally of the tube. The reinforcing partition is thenextruded integrally with the tube.

The present invention provides a first liner for pressure vessels whichcomprises a trunk having an opening at each of opposite ends thereof,and a head plate joined to each of the opposite ends of the trunk andclosing the end opening of the trunk, the trunk comprising the extrudedtube having the modified joint portions and constituting the tubularmetal body of the invention.

The invention provides a second liner for pressure vessels whichcomprises a trunk having an opening at each of opposite ends thereof, ahead plate portion integral with one end of the trunk for closing theend opening of the trunk and having a mouthpiece mount portion, and ahead plate joined to the other end of the trunk and closing the otherend opening of the trunk, the trunk and the head plate portion beingprovided by machining one end portion of the extruded tube having themodified joint portions and constituting the tubular metal body of theinvention.

With each of the first and second liners for use in pressure vessels,high pressure resistance is given to the trunk and accordingly to theentire liner, and the liner is prevented from fracturing at the jointportions. The trunk is made from a die-extruded tube, is thereforeuniform in wall thickness and affords a liner of increased length orlarger size. Furthermore, liners of complex cross section can beprovided.

With the two liners of the invention for use in pressure vessels, thehead plate may be joined to the trunk by friction agitation.

With the two pressure vessel liners of the invention, the trunk isfixedly provided inside thereof with a reinforcing partition extendinglongitudinally of the trunk and dividing inside of the trunk into aplurality of spaces. The reinforcing partition is joined to the trunk byfriction agitation at at least two of the modified joint portions of theextruded tube constituting the trunk, or is extruded integrally with thecomponents of the extruded tube constituting the trunk. When the trunkis fixedly provided inside thereof with a reinforcing partitionextending longitudinally of the trunk and dividing inside of the trunkinto a plurality of spaces, further improved pressure resistance can begiven to the trunk, accordingly to the entire pressure vessel liner.

With the pressure vessel liner wherein the trunk fixedly has thereinforcing partition therein, the partition preferably has an endportion positioned toward the trunk end to which the head plate is to bejoined and projecting outward from the trunk, and the head plate isfitted around the projecting portion and joined to the trunk. Since thetrunk and the head plate are supported by the partition from inside inthis case, the parts can be joined with an improved work efficiencywhile the trunk and the head plate can be prevented from deforminginward when the parts are joined by friction agitation.

The present invention provides a third liner for pressure vessels whichcomprises a trunk having an opening at each of opposite ends thereof andtwo head plate portions formed integrally with respective opposite endsof the trunk for closing the end openings and each having a mouthpiecemount portion, the trunk and the two head plate portions being providedby machining opposite end portions of the extruded tube having themodified joint portions and constituting the tubular metal body of theinvention.

With the third pressure vessel liner of the invention, high pressureresistance is given to the trunk and accordingly to the entire liner,and the liner is prevented from fracturing at the joint portions. Thetrunk is made from a die-extruded tube, is therefore uniform in wallthickness and affords a liner of increased length or larger size.Furthermore, liners of complex cross section can be provided.

With the first to third pressure vessel liners of the invention, thejoint portions of the extruded tube constituting the trunk are modifiedpreferably by frictionally agitating each of the joint portions with aprobe of a friction agitation joining tool.

The present invention provides a fuel cell system comprising a fuelhydrogen gas pressure vessel, a fuel cell and pressure piping fortransporting fuel hydrogen gas from the pressure vessel to the fuel celltherethrough, the pressure vessel having one of the first to thirdliners described.

The invention provides a natural gas supply system comprising a naturalgas pressure vessel, and pressure piping for delivering natural gas fromthe pressure vessel, the pressure vessel having one of the first tothird liners described.

The present invention provides a first method of producing a liner forpressure vessels characterized by preparing a tube extruded through aporthole die and comprising a plurality of components joined to oneanother with a plurality of joint portions extending over the entirelength of the tube, placing a probe of a friction agitation joining toolfrom outside into each of the joint portions of the extruded tube so asto position the probe partly in the tube components on opposite sides ofthe joint portion, thereafter moving the extruded tube and the proberelative to each other longitudinally of the tube to therebyfrictionally agitate the base material metal of the extruded tube for amodifying treatment to produce finely divided crystal grains and obtaina trunk having an opening at each of opposite ends thereof, andsubsequently joining a head plate to each end of the trunk.

The present invention provides a second method of producing a liner forpressure vessels characterized by preparing a tube extruded through aporthole die and comprising a plurality of components joined to oneanother with a plurality of joint portions extending over the entirelength of the tube, placing a probe of a friction agitation joining toolfrom outside into each of the joint portions of the extruded tube so asto position the probe partly in the tube components on opposite sides ofthe joint portion, thereafter moving the extruded tube and the proberelative to each other longitudinally of the tube to therebyfrictionally agitate the base material metal of the extruded tube for amodifying treatment to produce finely divided crystal grains and obtaina trunk having an opening at each of opposite ends thereof, subsequentlyforming a head plate portion having a mouthpiece mount portion at oneend portion of the trunk integrally therewith and further joining a headplate to the other end portion of the trunk.

The first and second pressure vessel liners can be produced relativelyeasily respectively by the first and second production methods of theinvention.

In the first and second liner production methods of the invention, it isdesired that the base material metal of the tube as extruded from anextruder be frictionally agitated in each joint portion immediatelyafter extrusion. As in the case of the method of producing the tubularmetal body described, the liner can then be produced at a higher rate toachieve a higher production efficiency than when a porthole die-extrudedtube having its temperature lowered to a cold working level is used.Furthermore, it becomes possible to subject the liner produced to auniform solution heat treatment to result in stabilized mechanicalproperties. The operation described eliminates a faulty joint that wouldbe produced between the components of the tube in the initial stage ofextrusion.

In the first and second liner production methods of the invention, theextruded tube may have a reinforcing partition placed therein andextending longitudinally of the tube so as to divide inside thereof intoa plurality of spaces. In frictionally agitating the base material metalof the extruded tube in each of the joint portions thereof, the forwardend of the probe is placed into the partition through each of at leasttwo of the joint portions to join the partition to the extruded tube byfriction agitation and to form the trunk and fix the partition to thetrunk at the same time. This method then gives further improved pressureresistance to the trunk, and accordingly to the entire pressure vesselliner.

In the method of forming the trunk and fixing the reinforcing partitionto the trunk at the same time, the reinforcing partition has an endportion positioned toward the trunk end portion to which the head plateis to be joined and projecting outward from the trunk, and the headplate is fitted around the projecting portion and joined to the trunk.Since the trunk and the head plate are supported by the partition frominside in this case, the parts can be joined with an improved workefficiency while the trunk and the head plate can be prevented fromdeforming inward, for example, when the parts are joined by frictionagitation.

In the first and second liner production methods of the invention, theextruded tube may have a reinforcing partition interconnecting at leasttwo of the components thereof and extending longitudinally of the tube.The reinforcing partition is then extruded integrally with the tube. Themethod gives further improved pressure resistance to the trunk, andaccordingly to the entire liner.

In the method of extruding the tube and the reinforcing partitiontherein integrally therewith, the trunk end portion to which the headplate is to be joined is cut off to cause the reinforcing partition toproject outward from the trunk, and the head plate is fitted around theprojecting portion and joined to the trunk. Since the trunk and the headplate are supported by the partition from inside also in this case, theparts can be joined with an improved work efficiency while the trunk andthe head plate can be prevented from deforming inward, for example, whenthe parts are joined by friction agitation.

In the first and second liner production methods of the invention, thehead plate is butted against the trunk end portion to which the headplate is to be joined, a probe of a friction agitation joining tool isthen placed into the butted portion of the trunk and the head plate toposition the probe partly in the trunk and the head plate, and the trunkand the head plate are thereafter moved relative to the probe to movethe probe along the butted portion over the entire circumference thereofand join the head plate to the trunk by friction agitation.

The present invention provides a method of producing a liner forpressure vessels characterized by preparing a tube extruded through aporthole die and comprising a plurality of components joined to oneanother with a plurality of joint portions extending over the entirelength of the tube, placing a probe of a friction agitation joining toolfrom outside into each of the joint portions of the extruded tube so asto position the probe partly in the tube components on opposite sides ofthe joint portion, thereafter moving the extruded tube and the proberelative to each other longitudinally of the tube to therebyfrictionally agitate the base material metal of the extruded tube for amodifying treatment to produce finely divided crystal grains and obtaina trunk having an opening at each of opposite ends thereof, andsubsequently forming a head plate portion having a mouthpiece mountportion at each of opposite end portions of the trunk integrallytherewith.

The third pressure vessel liner described can be produced relativelyeasily by the third production method of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a fragmentary perspective view showing a tubular metal bodyaccording to Embodiment 1 of the invention.

FIG. 2 is a fragmentary perspective view showing a method of producingthe tubular metal body of Embodiment 1.

FIG. 3 is an enlarged fragmentary sectional view showing the method ofproducing the tubular metal body of Embodiment 1.

FIG. 4 is a fragmentary perspective view showing a tubular metal bodyaccording to Embodiment 2 of the invention.

FIG. 5 is a fragmentary perspective view showing a method of producingthe tubular metal body of Embodiment 2.

FIG. 6 is an enlarged fragmentary sectional view showing the method ofproducing the tubular metal body of Embodiment 2.

FIG. 7 is a cross sectional view showing a tubular metal body accordingto Embodiment 3 of the invention.

FIG. 8 is a fragmentary perspective view showing a tubular metal bodyaccording to Embodiment 4 of the invention.

FIG. 9 is a perspective view showing a pressure vessel liner accordingto Embodiment 5 of the invention.

FIG. 10 is a view in longitudinal section of a high pressure vesselwherein the liner of Embodiment 5 is used.

FIG. 11 is a perspective view showing a method of producing the pressurevessel liner of Embodiment 5.

FIG. 12 is a perspective view partly broken away and showing a pressurevessel liner according to Embodiment 6 of the invention.

FIG. 13 is a perspective view showing a method of producing the pressurevessel liner of Embodiment 6.

FIG. 14 is a perspective view partly broken away and showing a pressurevessel liner according to Embodiment 7 of the invention.

FIG. 15 is a perspective view showing a method of producing the pressurevessel liner of Embodiment 7.

FIG. 16 is a perspective view showing a pressure vessel liner accordingto Embodiment 8 of the invention.

FIG. 17 is a perspective view showing a method of producing the pressurevessel liner of Embodiment 8.

FIG. 18 is a perspective view showing a pressure vessel liner accordingto Embodiment 9 of the invention.

BEST MODE OF CARRYING OUT THE INVENTION

Embodiments of the present invention will be described below withreference to the drawings. Throughout the drawings, like parts will bedesignated by like reference numerals and will not be describedrepeatedly.

In the following description, the term “aluminum” includes aluminumalloys in addition to pure aluminum.

Embodiment 1

This embodiment is shown in FIGS. 1 to 3.

FIG. 1 shows a tubular metal body according to Embodiment 1, and FIGS. 2and 3 show a method of producing the same.

With reference FIG. 1, the tubular metal body 1 comprises a portholedie-extruded tube 2 having a circular cross section and comprising aplurality of, more specifically four, components 2 b which are joined toone another with a plurality of, i.e., four, joint portions 2 aextending over the entire length of the tube. The metal serving as thebase material of the extruded tube 2 is subjected to a modifyingtreatment at each of the joint portions 2 a to produce finely dividedcrystal grains in a striplike portion having a specified width andincluding the joint portion 2 a. The modified portion is indicated at 3.

The die-extruded tube 2 is made, for example, from one of JIS A2000alloy, JIS A5000 alloy, JIS A6000 alloy and JIS A7000 alloy.

The base material is modified by friction agitation using a probe offriction agitation joining tool.

Incidentally, the cross sectional shape of the die-extruded tube 2 isnot limited to circular but may be in the form of an ellipse (notlimited to a mathematically defined elliptical form but including formswhich are nearly elliptical, e.g., oblong) or otherwise shaped.

The tubular metal body 1 is produced by the method to be described belowwith reference to FIGS. 2 and 3.

First, an extruder 5 equipped with a porthole die is used for extrudinga tube 2 comprising a plurality of components 2 a which are joined toone another with a plurality of joint portions 2 a extending over theentire length of the tube. Arranged outside the outlet of the extruder 5are friction agitation joining tools 6 which are equal in number to thenumber of joint portions 2 a of the tube 2 to be extruded and positionedin corresponding relation with the joint portions 2 a. Each of the tools6 comprises a solid cylindrical rotor 7 having a small-diameter portion7 a provided integrally therewith at a forward end thereof and extendingfrom the rotor axially thereof with a tapered portion providedtherebetween, and a pinlike probe 8 extending from the end of the rotorsmall-diameter portion 7 a axially thereof and integrally therewith andhaving a smaller diameter than the portion 7 a (see FIG. 3). The rotor 7and the probe 8 are made of a material harder than the die-extruded tube2 and having heat resistance to withstand the frictional heat to beproduced during joining.

With the extrusion of the tube 2 temporarily stopped, each of thefriction agitation joining tools 6 has its probe 8 placed from outsideinto an end portion of the corresponding joint portion 2 a of the tube 2as forced out of the extruder 5 immediately after extrusion so as to bepositioned partly in the tube components 2 b at opposite sides of thejoint portion 2 a while rotating the tool 6, with the shoulder of thesmall-diameter portion 7 a of the tool 6 around the probe 8 pressedagainst the outer peripheral surface of the die-extruded tube 2 (seeFIG. 3). At this time, the forward end of the probe 8 is positionedpreferably at a distance of at least 0.1 mm to not greater than ½ of thewall thickness of the tube 2, from the inner periphery of the tube 2. Ifthis distance is less than 0.1 mm, it is likely that a V-shaped groovewill be formed in the inner periphery of the tube 2 longitudinallythereof during the agitation mixing operation by the probe 8 to bedescribed later, and the tube 2 will not be satisfactory in pressureresistance. Alternatively if the distance is in excess of ½ of the tubewall thickness, the portion to be modified of the entire wall thicknessof the tube is small in thickness to entail the likelihood thatsufficient pressure resistance will not be available because thestrength, elongation and like mechanical properties of the joint portion2 a can not be fully improved. The tube 2 as extruded from the extruder5 immediately after extrusion retains the hot working temperature. Theshoulder of the small-diameter portion 7 a in pressing contact with thetube outer periphery ensures satisfactory agitation by preventing thesoft metal portion from scattering at the start of and during theagitation to be described below, further generating frictional heat bythe sliding movement of the shoulder on the tube 2 and softening theportion of the tube 2 in contact with the probe 8 and the vicinity ofthis portion to a greater extent while preventing formation of flashesor like irregularities on the outer periphery of the tube 2.

The extrusion of the tube 2 is then resumed to move the extruded tube 2and each friction agitation joining tool 6 relative to each other andthereby move the probe 8 along the joint portion 2 a longitudinally ofthe tube 2. The frictional heat generated by the rotation of the probe 8and the frictional heat generated by the sliding movement of theextruded tube 2 and the shoulder relative to each other soften the basematerial metal of the tube 2 in the joint portion 2 a and in thevicinity thereof (i.e., the region indicated by a chain line A in FIG.3), and the softened portion is agitated and mixed by being subjected tothe rotational force of the probe 8, further plastically flows to fillup a groove left by the passage of the probe 8 and thereafter rapidlyloses the frictional heat to solidify on cooling. These phenomena arerepeated with the movement of the probe 8 to frictionally agitate, mixand modify the base material metal in the joint portion 2 a and thevicinity thereof, producing finely divided crystal grains. In this way,a tubular metal body 1 is continuously produced.

The tubular metal body 1 described is produced by continuously extrudingthe tube 2 and cutting the tube into specified lengths. The tubularmetal body 1 produced last has bores formed at the position where theprobes 8 are withdrawn, so that the portion having these bores is cutoff. In producing the last metal body 1, a contact member is disposed atthe end face of the tube 2 as completely forced out of the extruder inthe position corresponding to the join portions 2 a, and the probes 8are removed after being brought to the location of the contact member.This eliminates the bores to be produced in the metal tube 1 bywithdrawing the probes 8.

According to Embodiment 1, the probes 8 of friction agitation joiningtools 6 are used for modifying the joint portions 2 a of thedie-extruded tube 2 immediately after extrusion while the tube retainsthe hot working temperature. However, this mode of modifying treatmentis not limitative; the joint portions 2 a of the die-extruded tube 2 maybe modified after the tube has been extruded and spontaneously cooledsubsequently.

Embodiment 2

This embodiment is shown in FIGS. 4 to 6.

FIG. 4 shows a tubular metal body according to Embodiment 2, and FIGS. 5and 6 show a method of producing the tubular metal body.

With reference to FIG. 4, the tubular metal body 10 comprises a portholedie-extruded tube 2 which is fixedly provided inside thereof with areinforcing partition 11 extending over the entire length thereof anddividing the interior of the body 10 into a plurality of spaces. Thetube 2 and the partition 11 have the same length and have theircorresponding ends at the same position. The reinforcing partition 11comprises four integral partition walls 11 a extending radially from thecenter line of the tube 2 and equal in number to the number of jointportions 2 a, and is in the form of a cross in cross section. Each ofthe partition walls 11 a has an outer end joined by friction agitationto the tube 2 at the joint portion 2 a. The reinforcing partition 11 ismade, for example, from one of JIS A2000 alloy, JIS A5000 alloy, JISA6000 alloy and JIS A7000 alloy.

The die-extruded tube 2 and the reinforcing partition 11 may be madefrom the same material or different materials.

The partition 11 shown in FIG. 4 comprises partition walls 11 a whichare equal in number to the number of joint portions 2 a of the tube 2and which are joined to the tube 2 at all the joint portions 2 a,whereas the partition is not limited to this structure. The number ofpartition walls 11 a may be smaller than that of joint portions 2 ainsofar as the interior of the tube 2 can be divided into a plurality ofspaces by the walls. In this case, the partition walls 11 a are joinedto the tube 2 at the joint portions 2 a which are positioned as opposedto the walls 11 a and which are included among all the joint portions 2a.

The tubular metal body 10 is the same as the metal body 1 of Embodiment1 with the exception of the above feature.

The tubular metal body 10 is produced by the method to be described nextwith reference to FIGS. 5 and 6.

First, a porthole die is used for extruding a tube 2 which comprises aplurality of components 2 b joined to one another with a plurality ofjoint portions 2 a extending over the entire length of the tube. Thetube 2 is cut into specified lengths. A reinforcing partition 11 is alsoextruded and cut into the same lengths as the tube 2.

The cut partition 11 is inserted into the cut extruded tube 2, with theouter ends of the partition walls 11 a positioned in register with therespective joint portions 2 a (see FIG. 5). At this time, the outer endsof the partition walls 11 a are brought into intimate contact with theinner peripheral surface of the extruded tube 2.

Subsequently, while rotating friction agitation joining tools 6, each ofthe tools 6 has its probe 8 placed from outside into an end portion ofthe corresponding joint portion 2 a of the tube 2 so as to be positionedpartly in the tube components 2 b at opposite sides of the joint portion2 a, with the shoulder of the small-diameter portion 7 a of the tool 6around the probe 8 pressed against the outer peripheral surface of thedie-extruded tube 2. At this time, the probe 8 is placed into the jointportion 2 a so that the probe end is brought into the partition wall 11a of the reinforcing partition 11 (see FIG. 6). The shoulder pressedagainst the outer peripheral surface of the tube 2 produces the sameeffect as previously described with reference to Embodiment 1.

The extruded tube 2 and each friction agitation joining tool 6 are thenmoved relative to each other to thereby move the probe 8 along the jointportion 2 a longitudinally of the tube 2, whereby the base materialmetal is frictionally agitated, mixed and modified in the joint portion2 a of the tube 2 and the vicinity thereof (i.e., in the regionindicated by a chain line B in FIG. 6) to produce finely divided crystalgrains as is the case with Embodiment 1. At the same time, the basematerial metal is softened at the outer end of the partition wall 11 a(i.e., in the region indicated by the chain line B in FIG. 6) with thefrictional heat generated by the rotation of the probe 8, and thesoftened portion is agitated and mixed by being subjected to therotational force of the probe 8, further plastically flows to fill up agroove left by the passage of the probe 8 and thereafter rapidly losesthe frictional heat to solidify on cooling. These phenomena are repeatedwith the movement of the probe 8 to join the tube 2 to the partitionwall 11 a. In this way, a tubular metal body 10 is continuouslyproduced.

In producing the tubular metal body 10, the bore to be formed in thebody by withdrawing the probe 8 can be eliminated by arranging contactmembers at opposite end faces of the tube 2 at positions correspondingto the joint portion 2 a, placing the probe 8 into one of the contactmembers to modify the joint portion 2 a and join the partition wall 11a, thereafter moving the probe 8 to the location of the other contactmember, and withdrawing the probe. The contact members for the probe 8to be placed in is not always necessary.

Embodiment 3

FIG. 7 shows this embodiment.

With reference to FIG. 7, the embodiment, i.e., a tubular metal body 15,comprises a porthole die-extruded tube 2 which is elliptical in crosssection. The metal body 15 has the same structure as the metal body 10of Embodiment 2 with the exception of the above feature and is producedby the same method as the metal body 10 of Embodiment 2.

Embodiment 4

This embodiment is shown in FIG. 8.

FIG. 8 shows a tubular metal body 20 according to this embodiment. Thebody 20 comprises a porthole die-extruded tube 2 which is providedinside thereof with a reinforcing partition 21 extending over the entirelength of the tube 2 and formed integrally therewith so as to divide theinterior of the tube 2 into a plurality of spaces. The reinforcingpartition 21 is in the form of a cross in cross section and comprises aplurality of partition walls 21 a integral with respective components 2b of the tube 2, extending toward the center line of the tube 2 andjoined on the center line. The partition 21 is extruded integrally withthe tube 2, and the partition walls 21 a are integral with therespective components 2 b and joined to one another on the center lineof the tube 2. This joint portion is indicated at 22.

The metal body 20 has the same structure as the tubular metal body 1 ofEmbodiment 1 with the exception of the above feature, and is produced bythe same method as the metal body 1 of Embodiment 1.

The tubular metal bodies 1, 10, 15 and 20 of Embodiments 1 to 4 areuseful for fuel cell systems comprising a pressure vessel for fuelhydrogen gas, a fuel cell and pressure piping for transporting the fuelhydrogen gas from the pressure vessel to the fuel cell, for use in thepressure piping. Such a fuel cell system is installed in fuel cell motorvehicles or used in cogeneration systems.

The tubular metal bodies 1, 10, 15 and 20 are useful for cogenerationsystems comprising a natural gas supply system, power generator andpower generator drive apparatus, the gas supply system comprising anatural gas pressure vessel and pressure piping for delivering naturalgas from the vessel, for use in the pressure piping for transportingnatural gas from the pressure vessel to the power generator driveapparatus.

The tubular metal bodies 1, 10, 15 and 20 are useful for natural gasmotor vehicles comprising a natural gas supply system and an engine foruse with natural gas as a fuel, the gas supply system comprising anatural gas pressure vessel and pressure piping for delivering naturalgas from the vessel, for use in the pressure piping for transportingnatural gas from the pressure vessel to the engine.

The tubular metal bodies 1, 10, 15 and 20 are useful for oxygen gassupply system comprising an oxygen gas pressure vessel and pressurepiping for delivering oxygen gas from the pressure vessel, for use inthe pressure piping.

However, the tubular metal bodies of the invention are not limited touse in such pressure piping systems.

Embodiment 5

This embodiment is shown in FIGS. 9 to 11.

FIG. 9 shows a liner of this embodiment for use in pressure vessels, andFIG. 10 shows a high-pressure hydrogen tank wherein the liner is used.FIG. 11 shows a method of producing the pressure vessel liner.

With reference to FIG. 9, the pressure vessel liner 30 comprises ahollow cylindrical trunk 31 having an opening at each of opposite endsthereof, and aluminum head plates 32, 33 joined to the respective endsof the trunk 31 and closing the end openings.

The trunk 31 is in the form of the tubular metal body 1 of Embodiment 1and comprises a porthole die-extruded tube 2 wherein the base materialof the tube in all the joint portions 2 a and in the vicinity thereof ismodified.

The two head plates 32, 33 are made by cutting or forging. One of thehead plates, 32, is integrally provided with a mouthpiece mount portion32 a. The two head plates 32, 33 are each made, for example, from one ofJIS A2000 alloy, JIS A5000 alloy, JIS A6000 alloy and JIS A7000 alloy.

The tube 2 providing the trunk 31 and the two head plates 32, 33 may allbe made from the same material, or at least two of them may be made fromdifferent materials.

The trunk 31 is metallically joined to the head plates 32, 33 by asuitable method. According to the present embodiment, the trunk 31 andthe head plates 32, 33 are joined at the butted portions by frictionagitation over the entire circumference thereof. The beads of theresulting joints are indicated at 34.

With reference to FIG. 10, the liner 30 is covered with afiber-reinforced resin layer 35, for example, of a resin reinforced withcarbon fibers over the entire periphery thereof except for themouthpiece mount portion 32 a, for use as a high-pressure vessel 36.

The liner 30 for use in pressure vessels is produced by the method to bedescribed below with reference to FIG. 11.

First, a trunk 31 is made from a porthole die-extruded tube 2 by themethod described with reference to Embodiment 1, i.e., by the frictionagitation mixing of the base material thereof in all joint portions 2 aand in the vicinity thereof to modify and produce finely divided crystalgrains. The trunk 31 is the same as the tubular metal body 1 ofEmbodiment 1.

On the other hand, a head plate 32 having a mouthpiece mount portion 32a and a head plate 33 having no mount portion are made by forging orcutting.

The large end of the head plate 32 is then butted against one end of thetrunk 31. These ends are flat-surfaced, and are butted against eachother in face-to-face contact. The trunk 31 and the head plate 32 areequal in wall thickness at the butted portion. Subsequently, a frictionagitation joining tool 6 in rotation has its probe 8 placed into thebutted portion of the trunk 31 and the head plate 32 at one part of thecircumference thereof. The rotor 7 and probe 8 of the tool 6 are made ofa material harder than the trunk 31 and the head plates 32, 33 andhaving heat resistance to withstand the frictional heat to be generatedduring joining.

At this time, the shoulder of the small-diameter portion 7 a of the tool6 around the probe 8 is pressed against the trunk 31 and the head plate32. The shoulder in pressing contact with the work produces asatisfactory joint by preventing the soft metal portion from scatteringat the start of and during the joining, further generating frictionalheat by the sliding movement of the shoulder on the trunk 31 and thehead plate 32 to soften the portions of the trunk 31 and the head plate32 in contact with the probe 8 and the vicinity thereof to a greaterextent while preventing formation of flashes or like irregularities onthe surface of the joint.

The trunk 31 and the head plate 32 are then moved relative to thefriction agitation joining tool 6 to thereby move the probe 8circumferentially of the butted portion. The frictional heat generatedby the rotation of the probe 8 and the frictional heat generated by thesliding movement of the trunk 31 and the plate 32 relative to theshoulder soften the base material metal of the trunk 31 and the headplate 32 in the vicinity of the butted portion, and the softened portionis agitated and mixed by being subjected to the rotational force of theprobe 8, further plastically flows to fill up a groove left by thepassage of the probe 8 and thereafter rapidly loses the frictional heatto solidify on cooling. These phenomena are repeated with the movementof the probe 8 to thereby join the trunk 31 to the head plate 32. Theprobe 8 returns to the position where the probe is placed in first aftermoving along the entire circumference of the butted portion, whereby thetruck 31 is joined to the head plate 32 over the entire circumference.At this time, beads are produced.

After returning to the position where the probe 8 is first placed intothe butted portion or after moving past this position, the probe 8 ismoved to the location of a contact member disposed at the butted portionof the trunk 31 and the head plate 32, where the probe 8 is withdrawn.The other head plate 33 is also joined to the trunk 31 in the samemanner as above. In this way, a liner 30 is produced for use in pressurevessels.

The high-pressure vessel 36 is produced with use of the liner 30 bycovering the liner 30 with a fiber-reinforced resin layer 35 over theentire periphery thereof except at the mouthpiece mount portion 32 a.

Embodiment 6

This embodiment is shown in FIGS. 12 and 13.

FIG. 12 shows a liner 40 of this embodiment, wherein a trunk 31 has areinforcing partition 11 fixedly provided inside thereof so as to dividethe interior of the trunk 31 into a plurality of spaces. The partition11 has a greater length than the trunk 31, and opposite ends of thepartition 11 project outward beyond opposite ends of the trunk 31. Twohead plates 32, 33 are fitted around the respective projecting ends ofthe partition 11 and joined to the trunk 31. The liner 40 has the samestructure as the liner 30 of Embodiment 5 with the exception of theabove feature.

Stated more specifically, the trunk 31 and the reinforcing partition 11are made by giving a greater length to the partition 11 in the tubularmetal body 10 of Embodiment 2 than to the porthole die-extruded tube 2thereof and causing opposite ends of the partition 11 to project outwardbeyond the respective ends of the extruded tube 2.

The pressure vessel liner 40 is produced by the method to be describedbelow with reference to FIG. 13.

A trunk 31 is formed and a reinforcing partition 11 is joined to thetrunk 31 by friction agitation at the same time in the same manner as inthe method of producing the tubular metal body 10 of Embodiment 2 withthe exception of giving a greater length to the reinforcing partition 11than to the porthole die-extruded tube 2 and inserting the partition 11through the tube 2 so as to cause opposite ends of the partition 11 toproject outward beyond the respective ends of the tube 2.

On the other hand, a head plate 32 having a mouthpiece mount portion 32a and a head plate 33 having no mount portion are made by forging orcutting.

Subsequently, the head plates 32, 33 are fitted around the respectiveprojecting ends of the partition 11 and butted against the ends of thetrunk 31. The two head plates 32, 33 are thereafter joined by frictionagitation to the trunk 31 in the same manner as is the case withEmbodiment 5. Since the trunk 31 and the head plates 32, 33 aresupported from inside by the reinforcing partition 11 during joining,the trunk 31 and the head plates 32, 33 are prevented from deforminginward.

According to the present embodiment, the trunk 31 and the reinforcingpartition 11 may be produced in the following manner. The partition 11to be inserted into a die-extruded tube 2 is made to have the samelength as the tube 2. The joint portions 2 a of the tube 2 are modifiedand the partition 11 is joined to the tube 2 at the same time in thesame manner as above, and opposite end portions of specified length arethereafter cut off from the tube 2, whereby the trunk 31 and thepartition 11 are produced.

Embodiment 7

This embodiment is shown in FIGS. 14 and 15.

FIG. 14 shows a pressure vessel liner 50 of this embodiment, wherein atrunk 31 has a reinforcing partition 11 provided inside thereofintegrally therewith so as to divide the interior of the trunk 31 into aplurality of spaces. The partition 11 has a greater length than thetrunk 31, and opposite ends of the partition 11 project outward beyondopposite ends of the trunk 31. Two head plates 32, 33 are fitted aroundthe respective projecting ends of the partition 11 and joined to thetrunk 31. The liner 50 has the same structure as the liner 30 ofEmbodiment 5 with the exception of the above feature.

Stated more specifically, the trunk 31 and the reinforcing partition 11are made from the porthole die-extruded tube 2 of the tubular metal body20 of Embodiment 4, by cutting off the opposite end portions of the tube2 over a specified length.

The pressure vessel liner 50 is produced by making a trunk 31 and areinforcing partition 21 in the same manner as in the method ofproducing the tubular metal body 20 of Embodiment 4, thereafter cuttingoff the opposite end portions of the die-extruded tube 2 over aspecified length, and subsequently joining two head plates 32, 33 toopposite ends of the trunk 31 by friction agitation in the same manneras is the case with Embodiment 6 (see FIG. 15).

Embodiment 8

This embodiment is shown in FIGS. 16 and 17.

FIG. 16 shows a pressure vessel liner 60 of this embodiment, wherein atrunk 31 has a head plate portion 61 formed integrally with one endthereof and having a mouthpiece mount portion 61 a. One opening of thetrunk 31 is closed with this head plate portion 61. No portion of areinforcing partition 11 extends into the interior of the head plateportion 11. The liner 60 has the same structure as the liner 40 ofEmbodiment 6 with the exception of the above feature.

Stated more specifically, the trunk 31 and the reinforcing partition 11are made by positioning one end of the reinforcing partition 11 of thetubular metal body 10 of Embodiment 2 inwardly of one end of theporthole die-extruded tube 2 thereof and causing the other end of thepartition 11 to project outward beyond the other end of the tube 2.

The pressure vessel liner 60 is produced by the following method.

A trunk 31 is made, and a reinforcing partition 11 is joined to thetrunk 21 by friction agitation at the same time, by the same method asEmbodiment 6 with the exception of positioning one end of the partition11 inwardly of one end of the porthole die-extruded tube 2 (see FIG.17), and a head plate portion 61 having a mouthpiece mount portion 61 ais thereafter formed by spinning, forging or pressing the projecting endof the trunk 31. A head plate 33 is subsequently joined to the other endof the trunk 31 in the same manner as in the case of Embodiment 6. Inthis way, a pressure vessel liner 60 is produced.

With the method described above, the joint portions 2 a of thedie-extruded tube 2 providing the trunk 31 are modified to finely dividethe crystal grains of the base material metal, with the result that thejoint portions 2 a are improved in elongation, strength and likemechanical properties. Accordingly, the trunk 31 can be subjected tospinning or press work or forged without permitting cracks to develop inthe joint portions 2 a. Unless the joint portions 2 a of the portholedie-extruded tube 2 are modified, spinning, forcing or press work islikely to cause the joint portions 2 a to develop cracks.

Embodiment 9

This embodiment is shown in FIG. 18.

FIG. 18 shows a pressure vessel liner 70 of this embodiment, wherein atrunk 31 has a head plate portion 71 integral with each of opposite endsthereof and having a mouthpiece mount portion 71 a. The head plateportion 71 closes an opening at each end of the trunk 31. The liner 70has the same structure as the line 30 of Embodiment 5 with the exceptionof the above feature.

Stated more specifically, s trunk 31 is made in the same manner as inthe case of Embodiment 1, and opposite end portions of the trunk 31 areworked by spinning, forging or pressing to provide respective head plateportions 71 each having a mouthpiece mount portion 71 a. In this way, aliner 70 is produced for use in pressure vessels.

In spinning the trunk 31 by this method, no cracks will develop in thejoint portions 2 a of the die-extruded tube 2 constituting the trunk 31as is the case with Embodiment 8.

With Embodiments 5 to 9, the cross sectional shape of the die-extrudedtube 2 is not limited to circular but may be in the form of an ellipse(not limited to a mathematically defined elliptical form but includingforms which are nearly elliptical, e.g., oblong) or otherwise shaped.

As is the case with Embodiment 5, the liners 40, 50, 60, 70 ofEmbodiments 6 to 9 are each covered with a fiber-reinforced resin layer,for example, of a resin reinforced with carbon fibers over the entireperiphery thereof except for the mouthpiece mount portion 32 a, 61 a or71 a for use as a high-pressure vessel.

The high-pressure vessel having any one of the liners 30, 40, 50, 60, 70of the foregoing embodiments is used in fuel cell systems comprising afuel hydrogen gas pressure vessel, a fuel cell and pressure piping fortransporting fuel hydrogen gas from the pressure vessel to the fuel celltherethrough, as the hydrogen gas pressure vessel. The fuel cell systemis installed in fuel cell motor vehicles. The fuel cell system is usefulalso for cogeneration systems.

Further the high-pressure vessel is used in natural gas supply systemscomprising a natural gas pressure vessel, and pressure piping fordelivering natural gas from the pressure vessel, as the natural gaspressure vessel. The natural gas supply system is used along with apower generator and a power generator drive apparatus in cogenerationsystems. The natural gas supply system is used also in natural gas motorvehicles comprising an engine for use with natural gas as a fuel.

The high-pressure vessel is used also in oxygen gas supply systemscomprising an oxygen gas pressure vessel, and pressure piping fordelivering oxygen gas from the pressure vessel, as the oxygen gaspressure vessel.

INDUSTRIAL APPLICABILITY

The invention provides tubular metal bodies for use in high-pressurepiping, for example, for motor vehicles, houses, transport machines,etc. for passing therethrough fuel hydrogen gas or natural gas of highpressure serving as a fuel for power generation. Such tubular metalbodies are used for providing trunks of liners for pressure vessels forstoring hydrogen gas, natural gas or oxygen gas in motor vehicles,houses and transport machines.

1. A method of producing a tubular metal body, comprising: preparing atube extruded through a porthole die and comprising a plurality ofcomponents joined to one another with a plurality of joint portionsextending over the entire length of the tube; placing a probe of afriction agitation joining tool from outside into each of the jointportions of the extruded tube so as to position the probe partly in thetube components on opposite sides of the joint portion; and moving theextruded tube and the probe relative to each other longitudinally of thetube to thereby frictionally agitate the base material metal of theextruded tube for a modifying treatment to produce finely dividedcrystal grains.
 2. A method of producing a tubular metal body accordingto claim 1 wherein the extruded tube has a reinforcing partition placedtherein and extending longitudinally of the tube so as to divide insidethereof into a plurality of spaces, and in frictionally agitating thebase material metal of the extruded tube in each of the joint portionsthereof, a forward end of the probe is placed into the partition througheach of at least two of the joint portions to join the partition to theextruded tube by friction agitation.
 3. A method of producing a tubularmetal body according to claim 1 wherein the extruded tube has areinforcing partition interconnecting at least two of the componentsthereof and extending longitudinally of the tube, the reinforcingpartition being extruded integrally with the tube.
 4. A method ofproducing a tubular metal body, comprising: preparing a tube extrudedthrough a porthole die and comprising a plurality of components joinedto one another with a plurality of joint portions extending over theentire length of the tube; placing a probe of a friction agitationjoining tool from outside into each of the joint portions of theextruded tube immediately after extrusion so as to position the probepartly in the tube components on opposite sides of the joint portion;and moving the extruded tube and the probe relative to each otherlongitudinally of the tube to thereby frictionally agitate the basematerial metal of the extruded tube for a modifying treatment to producefinely divided crystal grains.